R121 uses a different install method. If you have little experience, try Beta 3, which installs normally. If you want to get your hands dirtier, you can follow the r121 install instructions on the pdaXrom home (the page that loads when you enter www.pdaxrom.org s a URL) page (just replace the Cxx00 files with the Cxx0 files). Note that you have to install a new bootloader to use r121.